Several compounds among the 1,3-cyclohexanedione derivatives which are acylated at the 2-position with an arylcarbonyl group, have already been commercially available as agrochemicals. For example, mesotrione has attracted public attention as a foliar treatment type herbicide for maize. A 1,3-cyclohexanedione ring is tautomeric and exists also as 1-hydroxycyclohexen-3-one, which is an enol form thereof, and this derivative has been developed into various compounds for agrochemical use.
There have been reports on, for example, derivatives in which the aryl group of the arylcarbonyl group substituted at the 2-position has been changed to heteroaryl such as thiophene (see Patent Document 1), derivatives having the 1,3-cyclohexanedione ring fused at the 4- and 5-positions with a cyclopropane ring (see Patent Document 2), derivatives having the arylcarbonyl group at the 2-position changed to a pyrimidin-5-ylcarbonyl group derivative (see Patent Document 3), derivatives having the aryl carbonyl group at the 2-position changed to a pyrazin-2-ylcarbonyl group derivative (see Patent Document 4), derivatives having the arylcarbonyl group at the 2-position changed to a 1,2,3-thiadiazol-5-ylcarbonyl group derivative (see Patent Document 5), derivatives having the arylcarbonyl group at the 2-position changed to a pyridinecarbonyl group derivative (see Patent Documents 2, 6, 7, 8, 9 and 10), derivatives having the arylcarbonyl group at the 2-position changed to a quinolinecarbonyl group derivative (see Patent Documents 11 and 12), derivatives having the arylcarbonyl group at the 2-position changed to a heteroarylcarbonyl group derivative formed from a benzazole compound (see Patent Document 13), derivatives having the arylcarbonyl group at the 2-position changed to an azolecarbonyl group derivative formed from a 1,2-azole compound (see Patent Document 14), and derivatives having the arylcarbonyl group at the 2-position changed to a pyridonecarbonyl group derivative (see Patent Document 15). Furthermore, derivatives in which the 4-position and the 6-position of the 1,3-cyclohexanedione ring are crosslinked with an alkylene group such as an ethylene group, have also been reported (see Patent Documents 8, 11, 12, 13, 14, 16 and 17). There have been also reported derivatives in which the 1,3-cyclohexanedione ring has a substituted thiol group introduced at the 5-position (see Patent Document 18).
As such, a large number of cyclohexanedione-based compounds having a herbicidal activity have been reported, but there is no known cyclohexanedione-based compound having a dihydropyrazine ring substituted with an oxo group or a thioxo group (in the present specification, these groups may be collectively referred to as (thio)oxo), such as the compound of the present invention represented by formula [I] which will be shown below.